Nod32 all old virus updates and firewall

hello firends
i am a newbie so i don't know how to get maximum help form this fourm.for last few days i start using NOD32 Admin 2.5 version. and it update perfectly but my quetion is what about the old viruses updation don't i need all those updations to protect my pc from old vriuses.
nod32 works very fast and good than a nortan etc. but its virus updation folder always shown appr. 6mb in size is it fine because nortons singal update is appr. 12mb. is it only have bunch of virus definations. is it more vulnerable than a norton.
their is option a "mirror" what is that for? and how to use it? every time i click it it shown error "update atleast once to use this option".
my last quetion is nod32 don't have its own firewall. which firewall is best to run with nod32. (what about zone alarm).

PLZ HELP
if possible plz reply on my mail id
4funn2@gamil.com

thanx in advance